Takashi Ono

Takashi Ono (1928–2026) was a distinguished mathematician whose foundational work in algebraic number theory and arithmetic geometry left a lasting mark on the field. He served for many years as a professor of mathematics at Johns Hopkins University and was widely respected for both his scholarship and his mentorship.

Born in Japan in 1928, Ono earned his PhD from Nagoya University under the supervision of Shokichi Iyanaga. His early research quickly attracted international attention for its depth and originality. He made seminal contributions to the arithmetic theory of algebraic groups, particularly in the study of Tamagawa numbers, and his work has continued to influence research in number theory and arithmetic geometry for decades.

Early in his career, Ono was invited by J. Robert Oppenheimer, at the suggestion of André Weil, to be a visiting member of the Institute for Advanced Study in Princeton. He returned to the IAS on multiple occasions, reflecting the sustained international recognition of his work. He held faculty appointments at the University of British Columbia and the University of Pennsylvania before joining Johns Hopkins University in 1968. He served as a full professor at Johns Hopkins until his retirement at the age of 82 and remained intellectually engaged with mathematics well beyond that time. Over the course of his career, he supervised 22 PhD students, many of whom are now mathematicians at universities around the world.

Professor Ono was known as a careful and rigorous mathematician, as well as a generous and thoughtful mentor. Through his clarity of thought, high standards, and quiet dedication to the discipline, he influenced generations of students and colleagues. In recognition of his contributions, he was named a founding Fellow of the American Mathematical Society.

In addition to mathematics, Professor Ono had a lifelong love of music. As an undergraduate, he double majored in mathematics and music and especially enjoyed classical music, with a particular fondness for the piano.

Takashi Ono is survived by his wife, Sachiko Ono, and their three sons: Momoro Ono (Heejoung), Santa J. Ono (Wendy), and Ken Ono (Erika), as well as five grandchildren—Aspen, Juliana, Sage, Eugene, and Sarah. He is also survived by his sister Natsue.

He is remembered with deep respect by his family, colleagues, students, and the global mathematical community.